The present invention relates to a hydraulic control method of a marine reduction and reverse gear in a crash-go-astern operation for switching a clutch in the marine reduction and reverse gear from a forward set state to a reverse set state so as swiftly stop a ship traveling ahead.
In order to swiftly stop a traveling ship and to switch the ship from traveling ahead to traveling astern in some cases, an operation called a crash-go-astern operation for instantaneously switching a clutch of a marine reduction and reverse gear from a forward set state to a reverse set state (to be more precise, the clutch goes through a neutral state instantaneously at one time between the forward set state and the reverse set state) is carried out conventionally. In other words, by switching the clutch to one for reverse driving, a reverse driving force is applied to a propeller which is rotating forward to brake. However, because a load is suddenly applied to an engine when the clutch is switched from the intermediate neutral state to the reverse set state, there is a fear of stalling. Therefore, in prior-art control, a threshold value for avoiding stalling is asset for each degree of a set engine speed during execution of the crash-go-astern operation, the clutch which has been switched to the reverse set state is returned to the neutral state if an actual engine speed is lower than the threshold value, and the clutch is switched to the reverse set state after the actual engine speed increases to some degree. In another case, a certain threshold value with regard to an engine load is set, a state of the engine load is detected, the clutch is similarly returned to the neutral state if the engine load is over the threshold value when the crutch is switched to the reverse setting to show a state of an overload with a fear of stalling, and the clutch is returned to the reverse setting after the state of the engine load gets out of the overload state.
In these methods, however, the clutch is switched again to the neutral state if the actual engine speed exceeds the threshold value again or the engine shows the overload state again after the clutch has been returned to the reverse set state. When the clutch is in the neutral state, external forces other than water do not act on the ship, i.e., a braking force is not applied. Because engagement and disengagement of the clutch are repeated until the actual engine speed increases sufficiently or until the engine gets out of the overload state as described above, considerable time is required for stopping the ship and an essential purpose of the crash-go-astern operation, i.e., an abrupt stop of the ship cannot be achieved satisfactorily.
In the present invention, as a hydraulic clutch control method of a marine reduction and reverse gear in a crash-go-astern operation for switching operating means of a hydraulic clutch mechanism provided to the marine reduction and reverse gear from a forward setting to a reverse setting in a stroke so as to abruptly stop a ship traveling ahead, fitting pressure of a reverse driving clutch is maintained for a while at standby clutch pressure set between a minimum value and a maximum value and appropriate for avoiding stalling if it is judged that there is a fear of the stalling due to a shock of clutch switching in the operation and the fitting pressure of the reverse driving clutch is increased if it is judged that there is no fear of the stalling.
As described above, because the clutch is not brought into the neutral state completely but the reverse driving clutch is fitted at the standby clutch pressure in avoiding the stalling, the reverse driving force due to the clutch fitting is applied to the propeller which is rotating forward as a braking force and time required for stopping the ship can be shortened.
As timing of hydraulic control of the reverse driving clutch and judgement of stalling, in the first policy, the fitting pressure of the reverse driving clutch is first increased to the maximum value as a target when the operating means of the hydraulic clutch mechanism is switched to the reverse setting in the crash-go-astern operation and the fitting pressure is reduced to the standby clutch pressure if it is judged that there is the fear of the stalling in a process of increasing of the fitting pressure.
A threshold value of an engine speed is set as a criterion of judgement of a state in which there is the fear of the stalling and a detected engine speed and the threshold value are compared with each other.
It is also possible that a threshold value of a load applied to an engine is set and a detected degree of a load applied to the engine and the threshold value are compared with each other.
It is also possible that an engine speed and a ship velocity are detected.
It is also possible that the standby clutch pressure is increased and reduced repeatedly at or below the maximum value of the clutch fitting pressure as an upper limit to apply the braking force to the propeller in stages or to eliminate the load applied to the engine in stages.
The increase in the fitting pressure of the reverse driving clutch based on a judgement of a state in which there is no fear of the stalling may be carried out according to an increase in an engine speed or a reduction in an engine load. As described above, by automatically controlling to increase working hydraulic pressure of the reverse driving clutch, it is possible to save time and effort for a valve switching operation and to fit the reverse driving clutch in an optimum pressure increasing pattern to effectively apply the reverse driving force as the braking force to the propeller.
In the invention, in the crash-go-astern operation for switching operating means of a hydraulic clutch mechanism provided to the marine reduction and reverse gear from a forward setting to a reverse setting in a stroke so as to abruptly stop in traveling ahead, initial fitting pressure of a reverse driving clutch is calculated from certain criterion of judgement of a ship in advance before the switching to the reverse setting and the reverse driving clutch is set at the calculated initial fitting pressure when the operating means has been switched to the reverse setting.
As a result, the judgement for avoiding the stalling is made before the reverse setting to avoid a delay in control. Because the fitting pressure of the reverse driving clutch is set at the calculated initial fitting pressure as soon as the operating means is switched to the reverse setting, the stalling can be avoided and the effective reverse driving force as the braking force can be applied to the propeller to shorten time required for stopping the ship.
The criterion of judgement is a propeller speed when the clutch mechanism is switched from the forward setting to a neutral state by the crash-go-astern operation to make the judgement for avoiding the stalling before the reverse setting.
Furthermore, calculation of the initial fitting pressure is performed based on a setting map of the initial fitting pressure corresponding to the propeller speed detected in the neutral state and the map is formed based on a load characteristic intrinsic to a ship. In other words, by only detecting the engine conditions such as the engine load and the engine speed, it is impossible to judge the drop amount of the engine speed in fitting of the reverse driving clutch which is different depending on the characteristic of a ship load of each the ship and a deviation of the calculated initial fitting pressure from the actual proper value may be generated. In the invention, by forming the map based on the load characteristic intrinsic to the ship, the proper initial fitting pressure for each the ship can be set and the effective crash-go-astern operation can be achieved.
After the reverse setting, the initial fitting pressure is increased to a maximum value according to an increase in an engine speed. As described above, by automatically controlling to increase working hydraulic pressure of the reverse driving clutch, it is possible to save time and effort for a valve switching operation and to fit the reverse driving clutch in an optimum pressure increasing pattern to effectively apply the reverse driving force as the braking force to the propeller.
In order to cope with cases in which the load characteristic intrinsic to the ship cannot be specified or there is a deviation of an estimated value from an actual value, the estimated load characteristic intrinsic to the ship is corrected according to a drop amount of an actual engine speed when the reverse driving clutch is set at the initial fitting pressure and the map is corrected according to the corrected load characteristic.
Moreover, the correction of the load characteristic intrinsic to the ship is repeated until the drop amount of the actual engine speed when the reverse driving clutch is set at the initial fitting pressure converges into a target range to thereby form a more accurate map to achieve the effective crash-go-astern operation. In this case, it is also possible that the number of corrections of the load characteristic intrinsic to the ship is set in advance.
The load characteristic intrinsic to the ship may change due to secular changes and the like of the ship. Therefore, the correction of the load characteristic intrinsic to the ship is carried out again when the drop amount of the engine speed which has converged into the target range at one time deviates again from the target range.
Above and other objects, features, and effects of the invention will become apparent from the following descriptions based on the accompanying drawings.
FIG. 1 shows an oil hydraulic circuit of a marine reduction and reverse gear suitable for a crash-go-astern control according to the present invention.
FIG. 2 is a block diagram of a crash-go-astern control structure according to the invention.
FIG. 3 shows an engine speed and clutch hydraulic fluid over time during a prior-art crash-go-astern operation.
FIG. 4 shows an engine speed and clutch hydraulic pressure over time during the crash-go-astern operation when detection of the engine speed is used.
FIG. 5 is a flow chart of a clutch hydraulic control in the crash-go-astern operation based on detection of the engine speed according to the invention.
FIG. 6 shows a clutch lever signal value, an engine load, and the clutch hydraulic pressure over time during the crash-go-astern operation when detection of the engine load is used.
FIG. 7 is a flow chart of the clutch hydraulic control in the crash-go-astern operation based on detection of the engine load according to the invention.
FIG. 8 shows the clutch lever signal value, a ship velocity, and the clutch hydraulic pressure over time during the crash-go-astern operation when detection of the engine speed and the ship velocity is used.
FIG. 9 shows the clutch hydraulic pressure over time when standby clutch pressure is varied up and down.
FIG. 10 is a flow chart of the clutch hydraulic pressure control in the crash-go-astern operation based on detection of the engine speed and the ship velocity according to the invention.
FIG. 11 shows the clutch lever signal value, the engine speed, and the ship load (ship velocity) over time for explaining timing of judgement of the standby clutch pressure or initial fitting pressure for avoiding stalling.
FIG. 12 is a setting map of the initial fitting pressure corresponding to a propeller speed in neutral shifting in the crash-go-astern operation formed based on a characteristic of the ship load.
FIG. 13 is a control block diagram for carrying out clutch hydraulic pressure control by setting the initial fitting pressure based on the ship load.
FIG. 14 is a flow chart of a clutch pressure control in the crash-go-astern operation for setting the initial fitting pressure according to a detected propeller speed by using a map based on the ship load before reverse setting to control reverse clutch pressure according to the invention.
FIG. 15 shows the engine speed and the reverse clutch pressure over time from neutral setting to reverse setting during the crash-go-astern operation.
FIG. 16 shows the engine speed over time to show a drop amount of the engine speed.
FIG. 17 shows progression of the drop amount of the engine speed and the initial fitting pressure after respective correcting operations for causing the drop amount of the engine speed to converge into a target range.
FIG. 18 is a flow chart formed by adding a course of map correction based on correction of the ship load by reading the drop amount of the engine speed to a course of the control in FIG. 14.